1. Field of the Invention
The present invention generally relates to a display device and, more particularly, to pads for an LCD (Liquid Crystal Display) and a manufacturing method thereof.
2. Description of the Related Art
CRTs (Cathode Ray Tubes) have been the primary type of display device for instrumentation system monitors, information system terminals, and televisions. However, conventional CRTs have not been able to respond to the need to manufacture electronic products with reduced size and weight because CRTs are fundamentally large and heavy.
LCDs (Liquid Crystal Displays), which are relatively thin and light weight, have been developed to replace the conventional CRT. In recent years, LCDs have begun to play an important role as a flat-type display device, thereby increasing market demand for LCDs.
Generally, a low cost, high performance thin film transistor-LCD (TFT-LCD) employs a non-crystalline silicon thin film transistor as a switching element. Currently, most LCD development is directed toward high resolution systems such as SVGA (800×600) and XVGA (1024×768) as compared to VGA (Video Graphic Array; maximum resolution: 640×480 pixels). Consequently, development and application of the TFT-LCD industry have been accelerated due to increase in size and enhancement in resolution. As a result, there have been many attempts to increase manufacturing productivity and decrease cost by simplifying manufacturing processes and improving manufacturing yield.
The LCD uses an electrooptical property of liquid crystals that are injected into an inside of a panel. In contrast to a PDP (Plasma Display Panel), a FED (Field Emission Display), etc., the LCD can not emit light itself. Hence, an LCD is provided with a back light as a separate light source to evenly emit light onto a display surface, thereby displaying a picture on the LCD panel.
Conventional LCD pads will now be explained with reference to FIGS. 1 and 2. FIG. 1 is a sectional view of a gate pad of the conventional LCD, and FIG. 2 is a sectional view of a conventional data pad.
As shown in FIG. 1, the conventional gate pad comprise three areas: a pad contact area I, a grinding area II, and an ACF (Anisotropic Conductive Film) deposit area III. A pattern on the grinding area II is removed before the ACF is deposited. The pad contact area I is in contact with the grinding area II at one side and extends beyond the ACF deposit area III at another side. As such, the gate pad comprises a gate metal 13 formed on a substrate 11; a protective film 17 and a gate insulating film 15 having a plurality of contact holes thereon through which a portion of the surface of the gate metal 13 is selectively exposed, and being sequentially laminated on an upper part of the gate metal 13; a transparent metal layer 19 connected to the gate metal 13 through the contact holes; an ACF 21 formed on an upper part of the transparent metal layer 19 in the ACF deposit area III; and a tape carrier package (TCP) layer 23 formed on the ACF 21.
Here, the transparent metal layer 19 is made of a layer of a transparent conductive material, such as ITO (Indium Tin Oxide), for use as a pixel electrode of an active region. Accordingly, a gate signal can be inputted from the TCP layer 23 to be transmitted to the gate metal 13 through the ACF 21 and through the transparent metal layer 19 and then transmitted to a thin film transistor (not shown) disposed within the active region.
The transparent metal layer 19 is formed in the pad contact area I such that most portions of the transparent metal layer 19 are covered by the ACF 21. However, a portion F1 of the transparent metal layer 19 at a side of the active region is not covered by the ACF 21 and is exposed. Further, some parts of the contact holes, which serve as a passageway for transmitting the gate signal inputted from the TCP layer 23 to the gate metal 13, exist beyond the ACF deposit area III.
Furthermore, before the ACF 21 is deposited, the gate metal 13, the gate insulating film 15, the protective film 17 and the transparent metal layer 19 in the grinding area II are removed. When the grinding process is completed, there is formed a portion F2 in which sectional surfaces of the gate metal 13 and the transparent metal layer 19 are exposed to ambient air.
The LCD of FIG. 1 further shows a color filter substrate 32 facing the substrate 11, and a sealing compound 30 for bonding the substrate 11 to the color filter substrate 32.
As shown in FIG. 2, the structure of a data pad is similar to that of the gate pad with the exception that there is a different width of each pattern and pitch between the patterns. Accordingly, the data pad also comprises a pad contact area I, an ACF deposit area III, and a grinding area II. The pad contact area I contacts the grinding area II at one side and extends beyond the ACF deposit area III at the other side at a side of an active region.
As such, the data pad comprises a substrate 11; a source/drain metal 16 formed on an upper part of a gate insulating film 15; a protective film 17, formed on an upper part of the source/drain metal 16, having a plurality of contact holes through which a surface of the source/drain metal 16 is selectively exposed; a transparent metal layer 19, formed in the pad contact area I, connected to the source/drain metal 16 through the contact holes; an ACF 21 formed in the ACF deposit area III; and a TCP layer 23 formed on an upper part of the ACF 21. Therefore, a data signal inputted from the TCP layer 23 is transmitted to the source/drain metal 16 through the ACF 21 and through the transparent metal layer 19, and then transmitted to a thin film transistor (not shown) within the active region.
In the data pad, similarly to the gate pad, the transparent metal layer 19 exists within the pad contact area I. Most portions of the transparent metal layer 19 are covered by the ACF 21, but a portion F3 existing beyond the ACF deposit area III is exposed. The source/drain metal 16, the protective film 17 and the transparent metal layer 19 in the grinding area II are sequentially removed. When the grinding process is completed, there exists a portion F4, in which sectional surfaces of the source/drain metal 16 and the transparent metal layers 19 are exposed.
The conventional LCD pads have a number of disadvantages. For example, conventional LCD pads are prone to atmospheric corrosion or electrolytic corrosion.
If an electrical signal is applied to the gate pad to be operated, the sectional surfaces of the gate metal and the transparent metal layer exposed after the grinding process, or the portion of the transparent metal layer uncovered by the ACF may raise an electrochemical reaction which increases the possibility of atmospheric corrosion or electrolytic corrosion on a portion of the gate metal, thereby leading to damage of the gate pad. That is, the thin film transistor is damaged due to a fine electrical shock generated during the electrochemical reaction, and the resistance of the gate wiring increases due to the atmospheric corrosion and the electrolytic corrosion of the gate metal.
If an electrical signal is applied to the data pad to be operated, an electrochemical reaction may be induced in the sectional surfaces of the source/drain metal and the transparent metal layer exposed after the grinding process or the portion of the transparent metal layer uncovered by the ACF which increases the possibility of atmospheric corrosion or electrolytic corrosion on a portion of the source/drain metal, thereby leading to damage of the data pad. That is, the thin film transistor is damaged due to a fine electrical shock generated during the electrochemical reaction, and the resistance of the data wiring increases due to the atmospheric corrosion and the electrolytic corrosion of the source/drain metal.